The present invention relates to an information recording method to be applied to information recording apparatus, such as character producing apparatus, and particularly to an image information recording method employing a disc-shaped recording medium.
Referring to FIG. 1, there is shown a general outline of a reproducing mechanism of the recording method of this type. On the surface of a recording medium disc 2, which is driven to a predetermined rotating position by a motor 1, such as a pulse motor, a recording medium is attached and on the peripheral portion of the same surface, a scale with address marks 3 for determining the rotating position of the disc 2 is placed. Furthermore, on the surface of the recording medium disc 2, there are formed two rows of concentric tracks with different diameters, an outer track 4 and an inner track 5. Multiple hologram image information 6 and 7 are recorded on the respective tracks 4 and 5, with a predetermined pitch. An electro-optic pair comprising a light emitting element 8 and light receiving element 9 for optically detecting the address mark 3 is fixedly disposed in close proximity to the recording medium disc 2, with the disk 2 positioned therebetween. The light emitting element 8 and the light receiving element 9 and the motor 1 constitute a control servo-system for actuating the disc 2, whereby the disc 2 is driven and stopped at a predetermined position in accordance with an indicated operation order.
In front of the disc 2, there is disposed a laser generation apparatus 10 which faces the tracks 4 and 5. A laser L projecting from the laser beam generation apparatus 10 is directed selectively to the track 4 or to track 5 in accordance with a deflection order when it passes through a deflecting apparatus 11 comprising a light deflecting element or a galvanomirror.
The diffracted light of the image information 6 and 7 which is selectively illuminated by the above-mentioned illuminating operation, is received by a photoelectric conversion element 12 disposed fixedly in close proximity to the peripheral portion of the disc 2. As a result, the image information 6 or 7 comes out of the photoelectric conversion element in the form of an electric signal, so that the recorded information on the disc 2 is read and reproduced.
In this type of the disc 2, the image information 6 and 7 is recorded as shown in FIG. 2. For example, the image information 6, which may be ABC . . . LMN . . . , is recorded in the track 4, and as the image information 7, different information, such as abc . . . lmn . . . , is recorded in the track 5. Therefore, the above-mentioned conventional recording method has an advantage that information capacity is great. On the other hand, it has a shortcoming in that it is difficult to speed up the reading speed at the time of reproduction.
This is true because, at the time of each reading step, the address mark 3 is detected and access to a necessary rotating position of the disc 2 is then obtained. When necessary, transfer from one track to another has to be conducted with the laser diffracted, which also takes time. The time necessary for track transfer is as short as several msec, but the access operation time is as long as 10 msec or more.
This is because there is a limitation to the rotation speed of the disc 2 since the driving force of the drive motor 1 and the strength of the disc 2 are limited. Furthermore, the maximum rotation angle of the disc 2 at the time of the access operation is .pi.rad, for example, when reading is transferred from information A (or information a) to information L (or information l), while the minimum rotation angle of the disc 2 is zero when reading is transferred from information A to information a. Thus, the arithmetical mean of the rotation angle of the disc 2 is about .pi./2rad for each access rotation.
Referring to FIG. 4, in a character producing apparatus of the hologram disc rotating type, a hologram disc 101 with multiple patterns, such as characters, recorded thereon, is rotated and a laser from a laser producing apparatus 102 is directed onto a selected pattern of the patterns and the pattern ray is projected on a vidicon 103 which serves as a photoelectric conversion tube, so that electric signals corresponding to the received light pattern are produced.
In the case of a character producing apparatus of a microfilm disc rotating type, as shown in FIG. 5, a microfilm disc 104 is rotated and light is projected onto a selected pattern by an illumination light source 105. The pattern ray is projected on the vidicon 103 through an optical system 106, so that electric signals corresponding to the received light pattern are produced.
In the case of a character producing apparatus of the running hologram film running type, as shown in FIG. 6, a hologram sheet 107 is caused to run and a laser from the laser producing apparatus 102 is directed in a selected pattern through a deflection apparatus 108 and the pattern ray is projected on the vidicon 103, so that electric signals corresponding to the received light pattern are produced.
In each of these character producing apparatuses, the capacity for storing information is great and accordingly the cost of each bit is advantageously low. It is, however, necessary to establish access to the recording medium, such as the disc 101 or 104, or the sheet 107, accurately at the necessary position in accordance with a selected call for an information pattern.
To be more specific, when the access position of the recording medium varies, the position and the angle of the pattern ray on the light receiving surface of the vidicon 103 also vary. Consequently, omission or deformation of the produced signals occurs, which has an adverse effect on the conversion operation.
More specifically, as shown in FIG. 7, when the directions of the writing coordinates x-x, y-y of the received light pattern of a kanji deviate with respect to the direction of the coordinate direction of the beam scanning of the vidicon 103, X-X, and Y-Y, signals produced by the electric conversion are dislocated as shown in FIG. 8, and when such dislocated signals are printed by a dot type printer, such as an ink jet printer, a multi-stylus printer, and a wire dot printer, similarity of the pattern is not attained and the quality of the printed character form is lowered.
In some of the conventional character producing apparatuses of this sort, for example, in the techniques as disclosed in Japanese laid-open patent applications Nos. 49-81053 and 51-43641, a reference mark for indicating the inscripted position of the pattern is attached to each pattern and by reading the mark, the access position of the recording medium is adjusted. In this case, however, the inscription coordinates of the recording medium cannot be caused to coincide with the directions of the scanning coordinates of the scanning of the vidicon.
Particularly, in the case of information comprising line images, such as Chinese characters, good printing quality cannot be obtained by adjusting the access position.
By making the driving system of the recording medium more accurate, the access accuracy can be improved to some extent, but the apparatus becomes more expensive and is impractical.
Furthermore, a large quantity of information can be recorded in high density by the hologram recording method and recording and reproduction of information is comparatively easy.
In the hologram to be used as an information recording medium, information is usually recorded in a small area in the form of a Fourier conversion hologram and multiple holograms with small areas are arranged in a circle or concentrically on the recording medium.
Referring to FIG. 15, there is shown an example of an arrangement of holograms to be recorded. In the figure, a photosensitive plate 201 comprises a photosensitive layer formed on a transparent base plate which is circular and thin, such as a plastic material or glass. The central portion of the photosensitive plate 201 is fixed to a shaft of a motor 202 and is rotatable about an axis which passes the center of the photosensitive plate 201 and is perpendicular to the surface of the photosensitive plate 201.
A focussing lens 203 is placed on the front side of the photosensitive plate 201 and disposed so that the focal plane thereof coincides with the surface of the photosensitive plate 201 or is in close proximity to the surface of the photosensitive plate.
An original 204 of a transparent type carrier information. The character information comprises a single character or a group of characters or letters arranged in matrix form.
Hologram recording of character information is conducted as follows: With the photosensitive plate 201 stopped, the original 204 is placed between the photosensitive plate 201 and the focussing lens 203 and is disposed in close proximity to the focussing lens 203.
Under this condition, the original 204 is illuminated by coherent light 205 through the converging lens 203. The coherent light 205 is a parallel ray and when it passes through the focussing lens 203, it becomes a focussed ray by the focussing lens 203 and passes through the original 204 and is focussed on the peripheral portion of the photosensitive plate 201 in the form of a spot as an object light. At the same time, the spot-like focused portion is illuminated by a reference light 206 capable of interfering with the object light. The reference light 206 is a parallel ray whose spot diameter is adjusted to be almost the same as that of the spot-like focused portion. The reference light 206 is caused to enter the photosensitive plate 201 from the same side as that of the object light.
The object light and the reference light 206 interfere with each other and the formed interference fringes are recorded on the photosensitive plate 201.
When recording is completed, the illumination light 205 and the reference light 206 are turned off and the plate 201 is rotated by a predetermined small angle by the motor 202 and is then stopped. A stepping motor or a servo-motor is used as motor 202.
As the next step, the original 204 in FIG. 15 is replaced with an original having another character information and the above-mentioned recording process is repeated. By repetition of such recording process, holograms with small areas are recorded in a circle in the peripheral portion of the photosensitive plate 201.
By performing necessary treatments, such as development, fixing and bleaching, of the thus recorded photosensitive plate 201, a recording member 201A as shown in FIG. 16 can be obtained.
In each of the multiple small area holograms H-1, H-2, H-3, . . . H-i, particular character information is recorded and the holograms are arranged circlewise on the recording member 201A.
The holograms can be arranged as shown in FIG. 17, with the holograms H.sub.1 -1, H.sub.2 -1, H.sub.3 -1, H.sub.1 -2, . . . H.sub.3 -i arranged concentrically in a recording member 201B. A circular shape formed by holograms arranged circlewise or concentrically is called a hologram circle, and the axis which passes through the hologram circle and which is perpendicular to the surface of the recording member is called a central axis of the hologram circle.
Referring to FIG. 18, there is shown the operation of reproduction of the recorded character information.
A central portion of the recording member 201A is fixed to a drive shaft of a motor 207 and is rotatable about the central axis of the hologram circle by the drive of the motor 207.
A reproduction light 209 is a ray of coherent parallel light having almost the same beam sectional area as that of the area of the small area hologram and is projected from a predetermined direction. When the reproduction light 209 illuminates the hologram H-j, for example, an image 204I of the character information recorded in the hologram H-j is reproduced by the diffracted light produced by the hologram H-j.
An image sensor 208 is disposed with the reading surface thereof coinciding with the reproduction position of the image 4I.
In FIG. 18, the position which is occupied by the hologram H-j is called the reproduction position and can be determined solely in the space of the apparatus.
When reading one character of the character group recorded in the hologram H-k in the character producing apparatus is necessitated, the character to be read is detected and when it is found that the character is recorded in the hologram H-k, a signal is applied to the motor 207 (stepping motor or servo-motor), so that the motor 207 rotates the recording member 201A in accordance with the signal, bringing the hologram H-k to the reproduction position. When this condition is realized, the reproduction light 209 is projected and the character information recorded in the hologram H-k is reproduced on the reading plane of the image sensor 208. In the meantime, a signal for indicating the position of the character to be read out of the reproduced character group is applied to the image sensor 208 and in accordance with the signal, the image sensor 208 selectively scans the character to be read and such scanning is converted to a series of electric signals.
In the case where the recording member 201B in FIG. 17 is employed instead of the recording member 201A in the apparatus in FIG. 18, the following steps are taken: For instance, when reproduction of the character information recorded in the hologram H.sub.2 -1 is reproduced, the recording member 201B is rotated about the central axis of the hologram circle so that the holograms H.sub.1 -1, H.sub.2 -1, H.sub.3 -1, are brought into their reproduction area. The reproduction area here means an area where any one hologram of the above-mentioned three holograms can be selectively illuminated. The direction of the reproduction light may be the same with respect to any hologram circle or may be different with respect to each hologram circle. In any case, the position of the reproduced image is the same even when any hologram in the reproduction area is illuminated and the holograms are recorded so as to attain the above-mentioned requirement.
When the hologram H.sub.2 -1 on which the character information to be read is recorded is brought into the reproduction area, the hologram H.sub.2 -1 is selectively illuminated by the reproduction light and the character information is reproduced on the reading plane of the image sensor 208. After this, the characters to be read are converted to electric signals in the above-mentioned manner.
Conventionally, the holograms brought to the reproduction position or into the reproduction area are illuminated by the reproduction light in the manner as shown in FIG. 19.
The projecting direction of the reproduction light 209 is determined by adjusting the configuration of a reproduction light source 210 for projecting the reproduction light 209, and of a reflector 211. From the reproduction light source 210, a parallel laser beam with a predetermined beam diameter is projected as the reproduction light 209.
Spacing between the holograms arranged in the recording member for practical use is very small.
Therefore, when the incident position of the reproduction light is deviated from the reproduction position, the reproduction light may illuminate the adjacent two holograms at the same time. In this case, independent character informations are overlapped and the overlapped information is reproduced on the reading plane of the image sensor 208, so that the reading of a desired character cannot be performed.
Furthermore, when the incident angle of the reproduction light is deviated from a predetermined angle, the position of a reproduced image is also deviated from the reading plane. Therefore, the reading becomes impossible in this case. When the direction of the reproduction light projected from the reproduction light source 10 is deviated slightly from a predetermined direction, or the reflection angle of the reflector 211 is slightly deviated from a predetermined angle, the change of the incident position and incident angle of the reproduction light is amplified. Therefore, conventionally, an extremely high accuracy is required for the setting of the disposing position of the reproduction light source 210 and the reflector 211. Such an incovenience can be reduced to some extent by disposing the reproduction light source 210 in proximity to the recording member. However, there is some limit in designing the apparatus.